1. Field of the Invention
The invention relates to electromagnetic clutches and, more particularly, to an improved connecting structure between an armature plate and a stopper plate for reducing impact noise and vibration when the armature plate is attracted to a rotor.
2. Description of the Invention
Electromagnetic clutches are well known in the prior art and are often used for controlling the transfer of power to a compressor in an automobile air conditioning system. One such electromagnetic clutch is disclosed in U.S. Pat. No. 4,296,851 to Pierce. Such a conventional electromagnetic clutch is shown in FIGS. 1 and 2.
Referring to FIGS. 1 and 2, electromagnetic clutch assembly 10 selectively drivingly couples a refrigerant compressor in an automobile air conditioning system to a driving source. For purposes of explanation only, the right side of FIG. 2 will be referred to as the forward or front end, while the left side of FIG. 2 will be referred to as the rearward or rear end. Electromagnetic clutch assembly 10 includes clutch rotor 15, electromagnetic coil 20, housing 21 and bearing 16, which collectively generally constitute driving mechanism 100 of electromagnetic clutch assembly. Hub 24, leaf spring 27, stopper plate 28 and annular armature plate 26 generally constitute driven mechanism 201 (FIG. 1) of the electromagnetic clutch assembly.
Electromagnetic clutch 10 is fixedly coupled to compressor housing 11, which is provided with tubular extension 12 surrounding compressor drive shaft 13. Drive shaft 13 is supported for rotation within housing 11 along horizontal axis X by bearings (not shown). Hub 24, armature plate 26 and clutch rotor 15 rotate about axis X.
Clutch rotor 15 is made of a magnetic material, such as steel, and comprises an outer annular cylindrical portion 151, an inner annular cylindrical portion 152 and an axial end plate portion 153 which connects outer and inner annular cylindrical portions 151 and 152 at their forward ends. Thus, an annular U-shaped cavity 17 is defined by cylindrical portion 151, 152, and 153. A plurality of V-shaped grooves 18 are provided on the outer peripheral surface of outer annular cylindrical portion 151 for receiving belt (not shown) to couple rotor 15 to the output of the automobile engine (not shown). Rotor 15 is rotatably supported on tubular extension 12 of compressor housing 11 by bearing 16.
Axial end plate portion 153 includes one or more concentric slits 19 which are disposed on one or more concentric circles. These slits 19 define a plurality of annular or arcuate magnetic poles on the axial end plate portion 153.
Electromagnetic coil 20 is disposed in annular cavity 17 of clutch rotor 15. Electromagnetic coil supplies a magnetic flux (not shown) which attracts armature plate 26 to axial end plate portion 153 of rotor 15. Coil 20 is contained within annular magnetic housing 21. Housing 21 has a U-shaped cross section and is fixed to supporting plate 22, which is secured to the axial end surface of housing 11 by a plurality of rivets 221. A small air gap is maintained between magnetic housing 21 and clutch rotor 15.
Hub 24 comprises tubular member 241 which is secured tightly on the terminal end portion of drive shaft 13 by forcible insertion. Flange portion 242 extends radially from the front end of tubular member 241 and may be integrally formed with tubular member 241 or formed separately and affixed by a known securing method, such as welding. Relative rotation between hub 24 and drive shaft 13 is prevented by a key-keyhole mechanism 131 provided at the terminal end portion of drive shaft 13. Hub 24 is further secured to the terminal end portion of drive shaft 13 by nut 25 which is threaded on the terminal end of drive shaft 13. Annular shim 132 is disposed between a rearward end of tubular member 241 of hub 24 and annular ridge 132a. Ridge 132a is formed on the outer peripheral surface of the terminal end portion of drive shaft 13. The shim and ridge arrangement allows for the adjustment of air gap "1" between annular armature plate 26 and axial end plate portion 153 of rotor 15.
Armature plate 26, which is made of magnetic material, is concentric with hub 24, and has friction surface 26a which faces friction surface 153a of axial end plate portion 153 of rotor 15. Armature plate 26 has a plurality of elongated apertures 261 disposed along a circle, and is coupled to flange portion 242 of hub 24 by a plurality of leaf springs 27. Each leaf spring 27 is fixed at one end to armature plate 26 by rivet 31, and at the other end to the rearward surface of stopper plate 28. Stopper plate 28 is secured to flange portion 242 by rivets 29. Spacing member 30 and leaf spring 27 are positioned between stopper plate 28 and flange portion 242. By this arrangement, armature plate 26 may move relative to hub 24 along axis X upon the deflection of leaf springs 27.
A plurality of damper assemblies 33 are disposed between armature plate 26 and stopper plate 28. Each damper assembly 33 includes pin member 34 having flange portion 34a and shaft portion 34b. Shaft portion 34b axially penetrates annular elastic member 35, which is made of a synthetic rubber or a natural rubber or vibroisolating rubber. Elastic member 35 has one end bearing against flange portion 34a and another end bearing against armature plate 26. Pin member 34 is caulked at its reward end so as to slightly compress elastic member 35. Caulked portion 34c at the rearward end of shaft portion 34a of pin member 34 is disposed within cylindrical cavity 26b formed in friction surface 26a of armature plate 26.
When electromagnetic coil 20 is energized, magnetic flux is produced by electromagnet 21. Armature plate 26 is thus attracted to frictional surface 153a against the recoil strength of leaf springs 27. Rotational force from the automobile engine is then transmitted to armature plate 26 through rotor 15, and armature plate 26 rotates with rotor 15. Rotational force between armature plate 26 and rotor 15 is transferred by leaf spring 27.
In general, when armature plate 26 is attracted to rotor 15, rotor 15 is rotating at a relatively high speed in accordance with the rotation of the engine via the V-belt. In this situation, elastic member 35, which is positioned in hole 28a of stopper plate 28, moves in the rotational direction of drive shaft 13. As best seen in FIG. 3, the front side of elastic member 35 is compressed and the rear side of elastic member 35 expands in the rotational direction of armature plate 26. Such repeated application of force tends to crack elastic member 35 along the peripheral surface of pin member 34.
Further, impact force and vibration are usually produced when armature plate 26 is attracted to frictional surface 153a of rotor 15. The impact force and vibration is generally absorbed by deforming elastic member 35 so that the axial end portion thereof is compressed as shown in FIG. 4. The repeated compressive forces tend to deteriorate the absorptive ability of elastic member 35.
Furthermore, after armature plate 26 is attracted to rotor 15, the centrifugal force of drive shaft 13 causes elastic member 35 to move away from the center of drive shaft 13. The frictional contact between stopper plate 28 and elastic member 35 is increased due to the centrifugal force. According to these collective forces, elastic member 35 is forced toward the outer radial direction of contact with stopper plate 28, while being forced from hole 28a. The forces tend to create stress concentrations in the corner portions of elastic member 35, causing elastic member 35 to crack and sometimes even move out of hole 28a of stopper plate 28.